The present invention generally relates to data compression. More particularly, the invention is directed to apparatus and methods for compressing image type data while fully preserving the original information content.
Data compression, and particularly that which relates to image data, has been the subject of investigation for numerous years. In recent times, interest has been renewed and amplified as a consequence of the increasing use of graphics in computer workstations, and the associated storage of the voluminous data associated therewith. Another technology trend motivating the use of compression in data storage derives from the increasing use of high resolution and high color range video displays, with associated large increases both in pixel count and data per pixel.
Another aspect of data compression relates to preservation of information as may otherwise be degraded by imprecise compression and decompression apparatus and methods. For example, the increasing use of video imaging in medical fields, with the associated high resolution and high color range data, represents a source of information which must not only be amenable to storage, retrieval and transmission, but must when so managed fully preserve the original information content. Most existing apparatus and methods of compression fail in this regard, in that information content is exchanged for information volume.
Examples of apparatus and method for compressing image data appear in the prior art. U.S. Pat. No. 4,369,463 describes a quantizer which uses adjacent pixel information in an error feedback predictor to compress data. The article entitled Logarithmic Range Differential Pulse Coded Modulation, as appears in the IBM Technical Disclosure Bulletin, Vol. 29, No. 1, Jun. 1986, pp. 375-378, describes video image data compression in the manner defined by the title. The article entitled Vertical Reference Coding for Digital Gray-Level Images, as appears in the IBM Technical Disclosure Bulletin, Vol. 22, No. 7, December 1979, pp. 2980-2985, describes gray scale image data compression using vertical redundancy characteristics. U.S. Pat. No. 4,532,651 uses a gray scale filter to selectively and permanently remove the least significant bit of data, in reliance upon adjacent pixel information, to accomplish image compression. U.S. Pat. No. 4,546,385 compresses image data using bit planes and retaining gray scale data only at the edges of black/white regions as determined by a comparison of the bit planes. U.S. Pat. No. 4,725,885 compresses data using history data to adjust the selection of the reduced range of magnitudes assigned each pixel position. Lastly, recently issued U.S. Pat. No. 5,081,450 compresses video data by combining chrominance and luminance at individual adjusted larger levels of granularity.
The various approaches taken in such art accomplish degrees of compression at the expense of preserving the full content of the original information. As noted earlier, this lack of complete integrity between the data preceding compression and the data subsequent to decompression is unacceptable where, as in the case of medical imaging, the accuracy of the information content is crucial at particularized regions of the image.